Which type of estate does not automatically end when a stipulated event occurs?

The fee simple subject to a condition subsequent is a type of estate that may not automatically terminate when a stipulated event occurs. Instead, it allows the grantor to retain the right to reclaim ownership of the property if the specified condition is violated or if the stipulated event happens. This means that as long as the grantor takes action to recover the property after the condition has been breached, the estate does not end automatically; it only concludes at the discretion of the grantor.

In contrast, the other types of estates mentioned have different characteristics. A fee simple absolute is the most complete type of ownership with no conditions attached, meaning it does not terminate upon any event. A leasehold estate is usually tied to the duration of a lease agreement, which terminates when the lease term ends. An ordinary life estate terminates automatically when the life tenant dies, reverting the property to the remainderman or the grantor. Hence, the unique characteristic of the fee simple subject to a condition subsequent is that it does involve conditions but does not result in automatic termination, making it the correct answer for the question.